Untreated hypertension has been associated with cognitive impairment as well as with heart disease, strokes, and renal disorders. Although it is well known that many of the medical consequences of essential hypertension are dramatically reduced with adequate treatment, drug noncompliance is a major problem in treating hypertension. Drug noncompliance may be due, in part, to the side effects of antihypertensive drugs. One side effect reportedly is diminished mental acuity. Surprisingly, the effects of the antihypertensive drugs upon cognition have not been systematicaly examined. In a pilot study we have distinguished between the acute effects of propranolol and alpha methyldopa upon specific cognitive processes in normotensives. The purpose of the proposed study is to examine the chronic effects of three commonly used antihypertensive drugs upon specific measures of cognition (e.g., memory processes, spare capacity, reasoning, spatial ability, reaction time) in relationship to plasma drug levels among individuals aged 45-64 years with moderate essential hypertension. One goal of this study is to examine drug effects upon cognition in a situation similar to that employed in the clinical treatment of moderate essential hypertension. To that end, following a washout period, 120 hypertensives will complete a 32-week study involving three phases: (1) double-blind crossover (hydrochlorothiazide (hct) or placebo); (2) hct stabilization; and (3) combination drug therapy (hct plus propranolol; hct plus alpha methyldopa; or hct plus placebo).